In computer networks having a mixed information technology (IT) infrastructure, some client machines may require different operating systems (OSes) relative to other client machines on the same network. Examples of OSes include Linux, Windows or DOS to name just a few examples. In some networks, booting is performed using a preboot execution environment (PXE). PXE is an environment in which network computers may be booted via a network interface without regard to local OSes or storage devices such as local hard drives. Moreover, different client machines may need to boot different OSes from the same PXE server.
In such a network, managing a plurality of OSes on a single PXE server is a challenging problem. In known networks, different PXE OS images are hosted by the PXE server and client machines are booted based on the MAC address of a network card or IP range of the client system. If the MAC address or IP address of a client system changes, a PXE server side configuration change is required.
By way of example, a PXELINUX system will search for its config file on the boot server as follows. First, the system will search for the config file using the client universal unique identifier (UUID), if one is provided by the PXE stack. It should be noted that some basic input/output systems (BIOSes) do not have a valid UUID, and may substitute data such as all logical ones instead of data in standard UUID format using lower case hexadecimal digits. The system may then search for the config file using the hardware type using its address resolution protocol (ARP) type code and address, all in lower case hexadecimal with dash separators. For example, for an Ethernet (ARP type 1) with address 88:99:AA:BB:CC:DD, the system may search for the filename 01-88-99-aa-bb-cc-dd.
If no config file is found using these techniques, the system will search for the config file using its own IP address in upper case hexadecimal, e.g. 192.0.2.91->C000025B. The included program “gethostip” may be used to compute the hexadecimal IP address for any host. If a corresponding config file is not found using this technique, the system may remove one hex digit and try again. If the config file is not found, the system will eventually try looking for a file named “default” (in lower case).
The following list shows the order in which the config file will be searched for in a PXELINUX system having a boot file name of /mybootdir/pxelinux.0, a UUID of b8945908-d6a6-41a9-611d-74a6ab80b83d, an Ethernet MAC address of 88:99:AA:BB:CC:DD and an IP address of 192.0.2.91:
/mybootdir/pxelinux.cfg/b8945908-d6a6-41a9-611d-74a6ab80b83d/mybootdir/pxelinux.cfg/01-88-99-aa-bb-cc-dd/mybootdir/pxelinux.cfg/C000025B/mybootdir/pxelinux.cfg/C000025/mybootdir/pxelinux.cfg/C00002/mybootdir/pxelinux.cfg/C0000/mybootdir/pxelinux.cfg/C000/mybootdir/pxelinux.cfg/C00/mybootdir/pxelinux.cfg/C0/mybootdir/pxelinux.cfg/C/mybootdir/pxelinux.cfg/default
Known attempts to identify an OS to boot using PXE where the UUID is used to identify the system to boot are inflexible because each machine is tied to a specific OS. Systems that use a MAC address are disadvantaged because server-side configuration changes are required if the network adapter is changed. Systems that use the client's IP address are disadvantaged because server-side configuration changes are needed when an associated DHCP server assigns a different IP address to the client.